Beta-2-microglobulin (B2 M) is a low molecular weight protein biomarker in urine, used in detection of early impairment of proximal tubular function, often for biological assessment of exposure to uranium. Previous studies of beta-2-microglobulin have been hampered by small sample size, limiting ability to determine if amount, duration or chemical form of uranium affects the level of beta-2-microglobulin or other measures of urinary function. This study will explore uses of beta-2-microglobulin as a biomarker using laboratory data and occupational history information previously collected from a population of 2213 workers who formerly worked at a uranium processing plant. Specific Aims are: 1) Characterize the beta-2-microglobulin levels in this population, and to compare their beta-2-microglobulin levels to reference intervals established for a population of unexposed community residents from the same region; Evaluate the trend over time in workers with repeated measures, and the ability of beta-2-microglobulin to predict diminished renal function; 2) Describe the relationship between beta-2-microglobulin and other parameters of renal function (serum creatinine, blood urea nitrogen, urinary protein, blood and glucose in urine) and compare those relationships in workers to the unexposed population; 3) Characterize the historical uranium exposure to each worker by amount and duration of exposure, age at exposure, and chemical form of uranium; 4) Determine the exposure-effect relationship between parameters of uranium exposure and level of urinary beta-2-microglobulin, and levels of other measures of renal function; 5) Relate current urine uranium levels of 100 workers to historical exposure and beta-2-microglobulin level. Our access to this large population of workers with beta-2-microglobulin measures and detailed occupational history data, coupled with our knowledge of industrial processes at this site, provides a unique opportunity to study this biomarker. Understanding risk of renal disease and usefulness of beta-2-microglobulin as a biomarker will improve medical screening and intervention in aging US population workers with previous occupational uranium exposure.